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2015 OMIG Abstract 13

Photodynamic Therapy-Potential as Alternative/Adjunctive Therapy
for MRSA Keratitis?

Darlene Miller, Guillermo Amescua, Francisco Halili, Jr., Alejandro Arboleta, Heather Durkee, Mukesh Taneja, Karam Alawa, Mariela C. Aguilar, Harry W. Flynn and Jean-Marie Parel
Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami

Purpose: Increasing clinical and laboratory resistant Staphylococcus aureus isolates recovered from keratitis is problematic and part of the growing public health crisis in antibiotic resistance. Limited topical antibiotics compromise effective patient management and optimal outcomes. Our purpose is to update the increasing resistant trends and changing epidemiology of MRSA keratitis in South Florida and to highlight Rose Bengal photodynamic therapy (PDT-RB) as a potential therapeutic alternative for the treatment of Staphylococcus aureus keratitis. 
Methods:  Laboratory records were reviewed and convenience sets of Staphylococcus aureus keratitis isolates were analyzed for MRSA prevalence (1990-June-2015, N= 941), mec A type (N=60) and emerging co-resistance (N=196, 2011-June 2015) to common topical antibiotics. We evaluated combinations of the photosensitizer Rose Bengal (RB, concentrations .1%, .03%)  and light (activated-ambient and green-518 nm) vs no light (dark-unactivated) to kill or inhibit growth of  fluoroquinolone sensitive/resistant MRSA strains plated on nutrient agar (1.5 x 104 cfu/ml) post 30 minute exposure.
Results:  The prevalence of MRSA keratitis increased by 62% from base line (1990-1994, 13.4%) to 35.7% for the last 18 months (2014-June 2015). Eighty percent of the MRSA were healthcare associated, mecA, type II (USA100).  In vitro susceptibility to moxifloxacin was less than 90% for both MSSA (N=126, 81%) and MRSA (N=70, 9%). Co-resistance were more likely to be associated with MRSA isolates for erythromycin (93% vs 41%), gentamicin (7% vs 1%) and trimethoprim sulfa (10% vs 2%).  All isolates remain susceptible in vitro to vancomycin. At 24 hours, there was complete inhibition of both MRSA strains with the 0.1% RB under activated and unactivated conditions. Killing was observed only under activated conditions for the lower (0.03%) concentration.
Conclusions:  Options for treatment and management of keratitis due to both MSSA and MRSA isolates are becoming more restrictive. We confirm that healthcare is a major risk factor for MRSA keratitis. Photodynamic therapy with Rose Bengal was effective in vitro in killing and or inhibiting MRSA and could have in vivo applications.

None NIH Center grant P30EY14801, Research to Prevent Blindness

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